In recent years, there have been used an LED driving semiconductor apparatus for driving a light-emitting diode (referred to as an LED hereinafter), and an LED driving apparatus using the same. The LED driving apparatus according to a prior art will be described with reference to FIG. 10. FIG. 10 is a circuit diagram showing the LED driving apparatus according to the prior art.
The LED driving apparatus according to the prior art shown in FIG. 10 has a rectifying circuit 2 for rectifying an alternating current voltage from an AC power source 1, a smoothing capacitor 103, an LED 110, a switching current detecting element 111, an inductor current detecting circuit 112, a booster chopper 120, a feedback circuit 130, and an input voltage detecting circuit 140. The booster chopper 120 has an inductor 104, a diode 105 (the LED may also serves as the diode), a switching element 108 and a control circuit 106, and drives the LED 110 by a boosted direct current output.
The feedback circuit 130 detects an LED current flowing through the LED 110, and controls the control circuit 106 for controlling the switching element 108 of the booster chopper 120 in response to the detected signal. At this time, the control circuit 106 is controlled to average the LED current when observed in time domain which is longer than a cycle of a low frequency alternating current.
The switching element 108 is controlled to be in an ON state when the inductor 104 emits energy. The switching element 108 is controlled to be in an OFF state in response to a switching current value, or is controlled to be in the OFF state when a predetermined time is elapsed after the switching element 108 is controlled to be in the ON state.
The above LED driving apparatus according to the prior art was provided for obtaining a constant LED current, having a smaller input current strain, and having comparatively lower cost, by the above circuit configuration.
Patent document 1 is Japanese Patent Laid-open Publication No. 2001-313423.